Alloy steel and articles



Oct. 20, 1964 w. c. CLARKE, JR., ETAL 3,

ALLOY STEEL AND ARTICLES Filed Nov. 16, 1954 Chromium l5%-25/ Manganese 4 o 20/o Carbon .|5%.80% Phosphorus .|5/.35% lron, Remainder INVENTORS WILL/AM C CLARKE; JR GE'ORGE N GOLLER His AHorney United States Patent 3,153,589 ALLQY STEEL AND AR'liCLEd William (I. tClarlre, .lrz, Baltimore, Md, and George T.

Geller, 3220 hannon Drive, Baltimore, Md; said Qlarlre, .liz, assignor to Armco Steel Corporation, a

corporation of @hio Filed Nov. 1-6, 1954, Ser. No. 469,71 8 (Zlaims. (6i. 75-l26) Our invention relates to stainless steel and more particularly to high temperature duty austenitic stainless steel and various articles of manufacture fashioned of the same, especially internal combustion engine valves.

One of the objects of our invention is the provision of a hard and strong stainless steel which is essentially austenitic and which possesses hardness and strength at high temperatures and which is resistant to oxidation and scaling at high temperatures and which likewise is resistant to the combustion products of leaded fuels.

Another object is the provision of a stainless steel which is essentially austenitic and which lends itself to various forming operations and machining operations as in the production of a variety of high temperature articles and products, particularly internal combustion engine valves, valve parts, gas turbine parts and the like.

A further object of our invention is the provision of an internal combustion engine valve steel and valves which are hard and durable at temperatures on the order of 1400 F. and more, and which are resistant to the attack of lead oxide at such temperatures.

Other objects of our invention in part will be obvious and in part pointed out during the course of the description which follows.

Our invention accordingly consists in the combination of elements, composition of ingredients and in the articles and products manufactured thereof as described herein, the scope of all of which is indicated in the claims at the end of this specification.

The single figure of the accompanying drawing shows one form of internal combustion engine valve and the valve steel composition thereof coming within the scope of our invention.

As conducive to a better understanding of certain features of our invention it may be noted at this point that stainless steel generally is defined as containing about 10% to 35% chromium with or without nickel and with or without additions of other particular ingredients for special purposes with remainder being substantially all iron. And it should be noted that the stainless steel which are considered to be essentially austenitic usually contain nickel, this is the amounts of some 4% to 30%. These steels, of course, are expensive, particularly because of the high cost of nickel.

The demands for stainless steels which are capable of withstanding the effects of combustion products of leaded fuels, especially at high temperatures, are constantly increasing. These requirements especially apply to the exhaust valves for internal combustion engines, for valve seats, for liners and the like. The requirement also applies to various parts of the gas turbine where the combustion products of leaded fuels are to be encountered.

Under the severe operating conditions of an internal combustion engine many of the heretofore known stainless steels are inclined to pit and corrode much too rapidly for practical use when the combustion products of leaded fuels are encountered at the high temperatures of operation. And this type of pitting and corrosion occurs even in those steels which generally are considered to be corrosion-resistant and indeed are resistant to the corrosion effects of common acids such as nitric acid, sulfuric acid, fruit acids and atmospheric corrosion, either at room temperatures or high temperatures.

And even in those stainless steel internal combustion engine valves which adequately withstand the corrosive attacks of common low test gasoline there is the inclination to pit and corrode in the presence of the combustion products of the high test leaded fuels. Particularly, it is found that the combustion products of tetraethyl lead or other gasoline addition agent, which like tetraethyl lead forms a combustion product containing a lead oxide, give rise to the active corrosive attack which impairs the life of an internal combustion engine valve, especially an exhaust valve.

In the usual passenger automobile the internal combustion engine valves on the intake side frequently encounter temperatures up to about 700 F. But the exhaust valves encounter temperatures on the order of some 1100 F. to 1400" F. or even higher. And in the internal combustion engines of trucks, tractors and other heavy equipment even higher temperatures are encountered on the exhaust side, that is by the exhaust valves. The same generally is true of airplane engines. Valves and valve parts fashioned of low aloy steels, of course, are wholly inadequate because they fail to possess the required resistance to scaling and corrosion under the high operating temperatures encountered. Scaling, of course, prevents proper seating of the valve with the consequent leakage of hot gases which in turn quickly raises the valve seat temperatures to excessive values resulting in a burning away of the seat of the valve. The combustion products of the leaded gasolines accentuate that act.

An object of the present invention, therefore, is the provision of a comparatively inexpensive stainless steel, and manufactured articles and products fashioned of the same, which is strong and hard at high temperatures and which is resistant to the corrosive attack of lead oxide had as the result of the combustion of leaded fuels.

Referring now more particularly to the practice of our invention we find that a stainless steel which is substantially austenitic and which essentially consists of the ingredients, chromium, manganese and iron, to which phosphorus is added in certain particular critical amounts, is hard at high temperatures and at the same time is resistant to the attack of lead oxide. We find that this steel agehardens or precipitation-hardens to give the desired properties. The phosphorus content lies betwen .l5% and 35%. The steel also contains carbon and nitrogen and may contain nickel in substantial amounts where desired.

We consider that the phosphorus content is critical because amounts less than .15 fail to give adequate hardening. And amounts substantially exceeding 35% appear to form eutectic phosphides with a consequent loss of the malleability of the steel. With the excessive phosphorus contents hot-working properties such as rolling, drawing and the like, as well as hot-forming properties such as upsetting, extrusion and the like, drastically s-utfer.

The stainless steel of our invention more particularly contains about 15% to 25% chromium, 4% to 20% manganese, .l5% to .40% carbon, .15% to 35% phosphorus with the remainder substantially all iron. For cast steel products the carbon content may amount to .15% to .80%. Preferably in wrought products we employ a carbon content of .15% to .25% to assure good hot-working properties while retaining adequate response to heat treatment. Nitrogen also is present in amounts from incidental values up to .60%, preferably up to 30%. The sum of the nitrogen and the carbon contents amounts to at least 20%. Nickel usually is present and may amount to as much as 10% where desired.

Where desired there may be employed-sulfur up to .15% and molybdenum and/or tungsten up to 3.5%. Higher sulfur contents may not be had with such a high 8,1 3 manganese content. And larger amounts of tungsten and/ or molybdenum cause a loss in malleability.

The hot-workability of our steel is beneficially im-- proved by the introduction of boron in amounts up to 005%, values higher than this being purposely avoided because of a loss of hot-workability at the higher values.

An internal combustion engine valve according to our invention is shown in the accompanying drawing.

Our stainless steel is essentially austenitic and preferably the ferrite content does not exceed" 2% by volume.

In the steel of our invention the chromium content is fairly critical in that with lower chromium content the steel loses the necessary resistance to lead oxide and moreover the scaling resistance in air is considered to be inadequate. With a chromium content in excess of 25% we find no benefit to corrosion-resistance and as opposed to this the ferrite content becomes excessive and the steel loses its ability to respond to precipitation-hardenin The manganese content or" our steel is important and likewise fairly critical. With a manganese content of less than 4% the steel loses its austenitic character. And with a manganese content exceeding steel difiiculties are encountered in melting the steel in that the molten metal becomes objectionably corrosive to furnace refractories.

The critical nature of the phosphorus content is briefly referred to above. The presence of this ingredient within the amounts indicated is vital because without phosphorus within the amounts of .15% to 35% the steel does not suificiently precipitation-harden to give the essential properties.

The carbon content of our steel is quite critical because with less than .15 the steel does not acquire the desired hardness. And with amounts above .40% for wrought metal the steel suffers in ductility at elevated temperatures. We attribute this loss of ductility to the formation of eutectics with the phosphides in the steel. In any event the upsetting characteristics are found to suffer and so also the extrusion properties. No benefit is had in cast metal where the carbon content exceeds .80%.

Although nitrogen is an ingredient which is not essential to the steel of our invention we preferably employ nitrogen in amounts up to .60%, the particular amount of nitrogen in general corresponding to the amounts of chromium and manganese, that is with chromium and manganese on the high sides the nitrogen likewise is on the high side, and where the chromium and manganese contents are in the lower part of their ranges the nitrogen content likewise is in the lower part of its range. Actually the amount of nitrogen corresponds more to the amount of manganese than it does to the amount of chromium. In any event, however, the nitrogen content should not exceed .60% because substantially higher values tend to give gassy metal.

Nickel likewise is an ingredient which is not essential to the steel of our invention. It may, however, be employed in amounts up to 10%, this serving to stabil ze the austeni-tic structure. (3n occasion, however, a minimum of this ingredient is employed since we find that to some extent it detracts from the resistance of my steel to the attack of lead oxide.

In the steel of our invention chromium, manganese, carbon, nitrogen and nickel are so corr lated, one with the other, that the steel is essentially austenitic. Good hot-hardness, resistance to scaling and resistance to the combustion products of leaded gasoline are had. The steel is strong and yet possesses good formability. By

suitable hot-forming machining operations the metal is fashioned into internal combustion engine valves, valve seats, liners and the like, and where desired gas turbine nozzles and other turbine parts are made of the steel.

As specifically illustrative of the steel of our invention We have prepared a. steel essentially consisting of 21.40%

chromium, 10.34% manganese, 0.17% carbon, 0.210%

d phosphorus, 0.17% nitrogen, 0.12% nickel and remainder substantially all iron. It will be noted that the sum of the carbon and nitrogen contents amounts to 0.344%. The steel is essentially austenitic.

The steel also is found to have excellent resistance to corrosion by molten lead oxides as shown in the table presented below, giving weight losses of several samples of steel immersed in molten lead oxide at 1675 F, held in a clay crucible, this in terms of grams per square decimeter per hour. And it has good hardness at elevated temperatures, 119 Brinell at 1400 F. for the particular sample, this using a cold ball penetrator.

TABLE Comparative Corrosion Rates 0]" Stainless Steels in Molten Lead Oxide Weight loss,

Sample: gms./ sq./dc1n./hr.

From the comparative data given above it will be seen that the steel of our invention possesses excellent ressitance to the combustion products of the leading gasolines. Moreover, it will be seen that the steel acquires substantial hardness at high temperatures, higher hardness values being had with the higher carbon and nitrogen contents.

Thus it will be seen that We provide in our invention a stainless steel and various articles and products fashioned of the same, particularly including internal combustion engine valves, in which the objects hereinbefore noted, together with many practical advantages, are successfully achieved. It will be seen that the steel and manufactured products are well adapted to resist the combustion products of modern fuels. Moreover, it will be seen that the steel and products are hard at high temperatures and well adapted to Withstand the impact and wear encountered in actual practical use. The steel is comparatively inexpensive because it employs a minimum of the common alloying ingredient nickel.

As many possible embodiments may be made of our invention and as many changes may be made in the embodiment hereinbefore set forth it will be understood that all matter described herein or shown in the accompanying drawing is to be interpreted as illustrative and not as a limitation.

We claim as our invention:

1. Chromium-manganese stainless steel consisting essentially of 15% to 25% chromium, 4% to 20% manganese, .15% to .80% carbon, 15% to 35% phosphorus, nitrogen up to .60%, with the sum of the carbon and nitrogen contents from 20% to 1.40%, sulfur up to .15 alloy of the group consisting of molybdenum and tungsten up to 3.5%, boron up to .005 and remainder substantially all iron.

2. Qhromiurn-manganese stainless steel consisting essentially of 15% to 25% chromium, 4% to 20% manganese, .15% to 'l0% carbon, .15% to 35% phosphorus, and remainde substantially all iron.

3. Chromium-manganese stainless steel consisting essentially of 15% to 25% chromium, 4% to 20% manganese, .15% to 25% carbon, up to 30% nitrogen, .l5% to 35% phosphorus, and remainder substantially all iron.

4. Stainless steel consisting essentially of about 21% chromium, about 10% manganese, .15% to 25% carbon, .15 to 35% phosphorus, up to .60% nitrogen, and remainder substantially all iron.

5. Chromium-manganese stainless steelinternal combastion engine valves having substantial hardness at 1400 F. and substantial resistance to corrosion by lead oxide and consisting essentially of about to 25% chromiurn, 4% to manganese, .15% to .80% carbon, nitrogen up to 60% With the sum of the carbon and nitrogen contents from .20% to 1.40%, .15% to 35% phosphorus, and remainder substantially all iron.

6. Chromium-manganese stainless steel internal combustion engine valves having substantial hardness at I 1400 F. and substantial resistance to corrosion by lead oxide and consisting essentially of about 15% to chromium, 4% to 20% manganese, .15% to .40% carbon, nitrogen up to with the sum of the carbon and nitrogen contents from 20% to .70%, .15% to phosphorus, and remainder substantially all iron.

7. Chromium-manganese stainless steel internal combustion engine valves having substantial hardness at 15 1400 F. and substantial resistance to corrosion by lead oxide and consisting essentially of aoout 21% chromium, about 10% manganese, .15% to 25% carbon, 15%

References Cited in" the file of this patent UNITED STATES PATENTS 2,686,116 Schempp et a1 Aug. 10, 1954 2,698,785 Jennings Jan. 1, 1955 FOREIGN PATENTS 683,956 Germany Nov. 18, 1939 

1. CHROMIUM-MANGANESE STAINLESS STELL CONSISTING ESSENTIALLY OF 15% TO 25% CHROMIUM, 4% TO 20% MANGANESE, 15% TO 80% CARBON, 15% TO 35% PHOSPHORUS, NITROGEN UP TO 60%, WITH THE SUM OF THE CARBON AND NITROGEN CONTENTS FROM .20% TO 1.40%, SULFUR UP TO .15%, ALLOY OF THE GROUP CONSISTING OF MOLYBDENUM AND 